1. Field
Apparatuses and methods consistent with exemplary embodiments relate to a loudspeaker and an acoustic filter and an electronic apparatus employing the same, and more particularly, to a sound generation apparatus having a slit-firing structure and an electronic apparatus using the same.
2. Description of the Related Art
In recent years, as electronic apparatuses are slimmed, sound apparatuses require a structure suitable for use in a slim structure. For example, to install the sound apparatuses inside a thin electronic apparatus, various sound apparatuses are manufactured, such as a down-firing type, a back-firing type, and a slit-firing type, regardless of a radiation direction. The down-firing type is a type in which a speaker is mounted on a bottom of an electronic apparatus, and sound is emitted downward and transferred toward a front side through floor reflection, an example of which is a front speaker of a digital television (TV). The back-firing type is a type in which a speaker is mounted on a back of an electronic apparatus and sound is emitted backward and transferred toward a front side using refraction, an example of which is a woofer speaker of a digital TV. The slit-firing type is a type which emits sound through a slit provided in a speaker box using Huygens diffraction principle.
The slit-firing method can maximize a main beam width of a directional beam pattern of an existing speaker to ensure that sound is not uniformly transferred according to a location by a high frequency beam formation of the existing speaker. Further, the slit-firing type can implement a speaker system having clarity higher than the existing down-firing type or the existing back-firing type by minimizing sound decay characteristic degradation of an impulse response due to an interference between a direct sound and reflected sound inside a slit through minimization of a gap of the slit. A 2-way front speaker of a digital TV is an example of the slit-firing type.
However, since there are many cases in which the slit-firing type speaker is applied to an electronic apparatus without acoustic analysis, sound quality deterioration emerges.
In the slit-firing method, a space between a speaker diaphragm and a front reflecting plate and a geometric space of a sound emission part serve as an acoustic filter, such as a Helmholtz resonator, and the Helmholtz resonator functions as a kind of a low-pass filter to cause degradation in reproduction performance of a high frequency band in a speaker.
FIG. 1 is a graph illustrating an intensity of a sound signal for frequency bands of a slit-firing type speaker.
As illustrated in FIG. 1, in the slit-firing type, because a space between a speaker diaphragm and a front reflecting plate and a geometric space of a sound emission part serve as a Helmholtz resonator, a cut-off frequency band is generated after a mid-range.
To compensate, the slit-firing type is implemented as a 2-way, that is, a mid-range speaker and a tweeter.
FIG. 2 is a view illustrating a frequency band of a 2-way speaker to solve the cut-off frequency degradation.
As illustrated in FIG. 2, a 2-way speaker system is used to represent a high frequency band represented only by a mid-range speaker. To represent the high frequency band, a tweeter is used.
The tweeter is applied as a direct-firing type or a slit-firing type. When the tweeter is implanted with the slit-firing type like a mid-range speaker, a certain buffer zone for sound absorption is provided around a tweeter dome to minimize an interference effect of a high frequency band due to reflected sound inside a slit. A size of the buffer zone for sound absorption is determined to ¼ of a wavelength of a sound wave corresponding to a crossover (X-over) band of the tweeter.
However, since a cut-off frequency of a high frequency band in a mid-range is determined by the slit-firing structure of a mid-range speaker, the slit-firing structure has a great influence on the crossover band with the tweeter. Therefore, when the slit-firing structure of the mid-range speaker is designed without acoustic analysis, a reproducing band of the mid-range speaker is narrowed, and thus the tweeter has to reproduce a frequency of below a resonance point (fo) to reproduce a crossover band. Therefore, there is a need for a fundamental method for expanding a mid-range of a slit-firing type speaker system.
An existing slit-firing type speaker system has to implement a constant ground plane radiation condition in a bottom front of a slit radiation part to ensure a stable acoustic characteristic regardless of an installation location. Otherwise, various problems occur according to a floor reflection condition.
FIGS. 3(a)-(b) are views illustrating an intensity of a sound signal for frequency bands according to an installation location of a slit-firing type speaker.
In FIG. 3 (a), a slit-firing type speaker 30 lies on a left point of a table 31. When a sound radiating direction of the slit-firing type speaker 30 is a right direction, an emitted sound is affected by a tabletop 32 of the table 31.
It can be seen from a graph illustrated in FIG. 3 (b), when the slit-firing type speaker 30 is located on an inner portion of the table 31, an intensity of the sound signal is kept uniform. When the slit-firing type speaker 30 is located on an end of the table 31, an intensity of a sound signal is weakened in a partial section.
In the slit-firing type speaker, deformation in frequency flatness and a directional beam pattern, and dip/peak in a frequency response due to an interference according to refraction and scattering may occur according to a floor reflection condition. Therefore, there is a need for a speaker system having a ground plane radiation condition capable of maximizing an intensity of a sound signal.